1. Field of the Invention:
The present invention relates generally to a method of detecting the position of the edge of a glass ribbon being advanced on a bath of molten metal in a continuous process for manufacturing a float glass according to the well known float process, and to an apparatus for performing such method.
2. Description of the Prior Art:
In the known process for manufacturing a float glass which is commonly referred to as a float process, the glass is moved forwardly on the surface of a bath of molten metal in a ribbon form, and the glass is made flat while being advanced therein. The bath of molten metal is usually composed of tin or tin alloy and is contained in a long and narrow tank made of a refractory material. In order to prevent oxidation of the molten metal, a protective atmosphere composed of a non-oxidative gas, such as nitrogen containing a small amount of hydrogen, is maintained in the upper space of the bath container or tank. In such float methods, the molten glass being sustained at high temperature is thus continuously fed from a forehearth connected to a glass melting furnace and is advanced in a ribbon form along the bath of molten metal so as to process a flat and smooth and parallel surface, and then the glass ribbon is taken up from the bath and cooled.
In the operation of such a float process, it is quite important to be able to accurately determine the position of the advancing glass ribbon on the bath of molten metal within the tank. Especially when the molten glass is being fed around the hot end of the bath of molten metal and is being spread in its ribbon form, it is quite important to accurately determine the position of the edge of the glass ribbon, in order to accurately control the flow of the molten glass, to maintain the quality of the glass ribbon on the bath of molten metal and to maintain a stable operation. Heretofore, such detection of the position of the edge of the float glass ribbon has been performed by observing it through an industrial television or directly from a watching window in the tank of the bath of molten metal. However, the accuracy of such detection depends upon the experience and ability of the operator, and different positions may be detected by different observers. It has also been proposed to inject a gas from a nozzle against the edge of the glass ribbon and to measure the back pressure to more accurately detect the positions of the glass edge. In this method, however, the edge of the glass ribbon is cooled by the gas and molten metal is blown on the surface of the glass ribbon, so as to cause the disadvantages of distortion thereon and surface stains.